1. Field of the Invention
The present invention is directed to an ink printer head of the type composed of a stacked ink printer modules operating according to the edge-shooter principle and that are equipped with ink ejecting piezoelectric actuators.
2. Description of the Prior Art
Ink printer head of the above-described type are used in small, fast printers that are in turn a component of modern machines for franking postal matter or for printing addresses.
Differing from a standard office printer with line-by-line imprinting, the printing ensues in such smaller machines as a one-time franking imprint in one pass of the postal matter. The printing width determines the number of nozzles to be arranged in one column of the nozzle matrix, and thus also determines one dimension of the ink printer head. The capability of printing blocks having word and image characters is a feature available using such postage meter machines. Printer resolutions of approximately 200 dpi are required for assuring a good printing quality. This requires nozzle apertures having a width of 40 through 50 xcexcm. High demands are thus made on the precision of the nozzle division and the drive thereof. Given a standard block width of one inch, the adjustment error must be kept below 10 xcexcm.
German OS 42 25 799 discloses an ink printer head of the type initially described that is composed of a number of different modules, only one module thereof carrying the shared nozzle row at its end face. All modules have pressure chambers driveable by piezoactuators for ink ejection that are connected to the allocated nozzles via appropriately conducted channels. The connecting channels from module to module necessarily proceed orthogonally relative to the pressure chambers.
Although the advantage of only a single nozzle row is significant, the technological outlay for manufacturing the modules that differ from one another is still substantial.
Higher precision than that needed to produce the pressure chambers and a higher adjustment outlay are required for the connecting channels that proceed through a number of modules. The fact that the connecting channels have different lengths causes additional control problems. When the nozzles are manufactured of UV-sensitive glass in common with the ink channels using an etching technique, they consequently have a hydrodynamically disadvantageous, rectangular cross section that can only be manufactured in practice with a precision of xe2x89xa75 xcexcm.
German OS 31 17 028 discloses a print element for ink printer devices having cylindrical ink channels that proceed in the print element and are at least partially encompassed by piezotransducers. This print element is composed of a head part, a channel plate adjacent thereto and a nozzle plate. The ink channels proceed parallel to one another in the head part. The channel plate has ink delivery channels into which the ink channels discharge at the one side and that form discharge apertures at the other side, which are connected to allocated nozzle apertures of the nozzle plate. Although approximately identical ink path lengths and round nozzle apertures are achieved with this ink printer head, a head volume too large for the initially described utilization in a postal franking machine would be required in order to achieve an imprint of 192 dpi, because of the 192 tubular piezotransducers. It is also difficult to contact the piezotransducers and to achieve acoustic decoupling between neighboring pressure chambers.
An object of the present invention is to achieve a print head suitable for use in a small postal franking machine having manufacturing outlay in comparison to known print heads used for that purpose while preserving the required printing precision.
The invention is to provide an ink printer head of the type initially described that is composed of identical ink printer modules having plate-shaped piezoelectric actuators and wherein the channels from the pressure chambers to the nozzles are of approximately equal length and neighboring pressure chambers are suitably acoustically decoupled.
It is a further object of the invention to provide such a print head having nozzles with a circular cross section produced more precisely then previously.
The above object is achieved in accordance with the principles of the present invention in an ink printer head formed by a number of side-by-side edge shooter ink printer modules forming a module assembly with a front side, each ink printer module having ink chambers therein open toward the front side of the assembly and being arranged in two columns with a slight spacing between the columns, an adapter plate covering the front side of said assembly and having openings therein in registry with the openings of the ink chambers in the respective ink printer modules, and a nozzle plate having nozzle apertures therein disposed over the adapter plate, the nozzle apertures being arranged in columns in the nozzle plate with the individual nozzle apertures disposed equidistantly from each other in each column and being offset from column-to-column so that no nozzle aperture is aligned with another nozzle aperture in a direction orthogonal to the column direction. The openings of the ink chambers in the front side of the assembly have a first dimension and the nozzle apertures have a second dimension which is smaller than the first dimension. The openings in the adapter plate have a first region having the first dimension and a second region having the second dimension. The openings in the adapter plate are disposed so that the respective first regions of the openings are in registry with the openings of the ink chambers and the respective second regions are in registry with the nozzle apertures.
In a preferred embodiment, each ink printer module has a pair of columns of openings in the adapter plate associated therewith. Since the nozzle openings in each ink printer module are arranged in two columns with a slight spacing between the columns, the pair of columns of openings associated with that ink printer module in the adapter plate is formed by one column of openings each having their first region in registry with one column of ink chamber openings, and the other column of openings in the pair each has its first region aligned with the respective ink chamber openings in the other column of the ink printer module. The respective smaller regions of the adapter plate openings in each column pair are meshed, so that those smaller regions, in turn, form a column. The column of smaller regions in each pair of adapter plate opening columns are in registry with the column of nozzle apertures in the nozzle plate allocated to that ink printer module.
Preferably ink is caused to be ejected from the ink chambers in an ink printer module by piezoelectric actuator, preferably a plate-shaped piezoelectric actuator. A number of advantages derive on the basis of the proposed arrangement.
Only one module type need be manufactured, preferably in a batch process. The number of ink printer modules in an ink printer head is based on the desired number of nozzles. A compact printer head structure with high packing density is achieved.
The adapter plate as well as the nozzle plate can be manufactured with high precision using a lithography technique. The openings in the adapter plate and the nozzle apertures in the nozzle plate can be manufactured in the same way with etching, laser drilling, sand blasting or LIGA technique. Punching would also be possible when the plates are steel. Only the thickness of the nozzle plate is critical for the nozzle length; all nozzles are thus of the same length.
The adapter plate fulfills a number of functions:
mechanical carrier of the thin nozzle plate
mechanical and fluid connection between ink printer module and nozzles
spatial matching between larger ink chambers and smaller nozzle apertures as well setting their spatial offset relative to one another
reduction of 2n columns of ink chambers to n columns of nozzles.
The dimensions of the openings in the adapter plate can be dimensioned such that ink paths of approximately equal length are present.
The problem areas of printer resolution and the precision of the nozzle division (equidistance) and nozzle shape has been displaced away from the modules themselves to the combination composed of the adapter plate and the nozzle plate and can be governed at those components without difficulty on the basis of lithography techniques.
The disclosed structure of the ink printer modules of a first cover plate, an intermediate plate, a second cover plate and a spacer plate makes it possible to place the ink chambers either in the cover plate or in the intermediate plate. The offset of the ink chambers at both sides of the intermediate plate with mismatch and the presence of the spacer plate effect a good acoustic decoupling within a module as well as among the modules. The spacer plate is expediently provided with recesses for the piezoactuators and their leads.
The connection between the nozzle and adapter plates as well as between the latter and the front surface of the module can ensue with UV-activatable adhesive that is previously applied in the lithography technique steps.
It is also possible to use thermal actuators within the ink chambers instead of the piezoactuators.